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        </div><article class="page single"><h1 class="single-title animated flipInX">Spring源码 - 声明式事务的挂起、提交、回滚、连接的释放原理</h1><div class="post-meta">
            <div class="post-meta-line"><span class="post-author"><a href="https://wlizhi.cc" title="Author" target="_blank" rel="noopener noreffer author" class="author"><i class="fas fa-user-circle fa-fw"></i>Wlizhi</a></span>&nbsp;<span class="post-category">收录于 <a href="/categories/spring/"><i class="far fa-folder fa-fw"></i>spring</a></span></div>
            <div class="post-meta-line"><i class="far fa-calendar-alt fa-fw"></i>&nbsp;<time datetime="2020-12-07">2020-12-07</time>&nbsp;<i class="fas fa-pencil-alt fa-fw"></i>&nbsp;约 4799 字&nbsp;
                <i class="far fa-clock fa-fw"></i>&nbsp;预计阅读 10 分钟&nbsp;<span id="/posts/spring/19-transaction-source-suspend-rollback-commit/" class="leancloud_visitors" data-flag-title="Spring源码 - 声明式事务的挂起、提交、回滚、连接的释放原理">
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  <ul>
    <li><a href="#1-事务的挂起">1 事务的挂起</a></li>
    <li><a href="#2-事务的提交">2 事务的提交</a></li>
    <li><a href="#3-事务的回滚">3 事务的回滚</a></li>
    <li><a href="#4-数据库连接的释放">4 数据库连接的释放</a></li>
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            </div><div class="content" id="content"><p>spring源码系列文章，示例代码的中文注释，均是 copy 自 <a href="https://gitee.com/wlizhi/spring-framework" target="_blank" rel="noopener noreffer">https://gitee.com/wlizhi/spring-framework</a> 。</p>
<p>链接中源码是作者从 github 下载，并以自身理解对核心流程及主要节点做了详细的中文注释。</p>
<hr>
<h2 id="1-事务的挂起">1 事务的挂起</h2>
<p>事务的挂起，调用的是 suspend()。</p>
<p>以下是 suspend() 源码：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">AbstractPlatformTransactionManager</span> <span class="kd">implements</span> <span class="n">PlatformTransactionManager</span><span class="o">,</span> <span class="n">Serializable</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">    <span class="kd">protected</span> <span class="kd">final</span> <span class="n">SuspendedResourcesHolder</span> <span class="nf">suspend</span><span class="o">(</span><span class="nd">@Nullable</span> <span class="n">Object</span> <span class="n">transaction</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">TransactionException</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="k">if</span> <span class="o">(</span><span class="n">TransactionSynchronizationManager</span><span class="o">.</span><span class="na">isSynchronizationActive</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">List</span><span class="o">&lt;</span><span class="n">TransactionSynchronization</span><span class="o">&gt;</span> <span class="n">suspendedSynchronizations</span> <span class="o">=</span> <span class="n">doSuspendSynchronization</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">			<span class="k">try</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="n">Object</span> <span class="n">suspendedResources</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">				<span class="k">if</span> <span class="o">(</span><span class="n">transaction</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="c1">// TODO 重点：如果存在事务，则挂起事务，其实就是从ThreadLocal变量中解绑连接。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>					<span class="n">suspendedResources</span> <span class="o">=</span> <span class="n">doSuspend</span><span class="o">(</span><span class="n">transaction</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 清楚TransactionSynchronizationManager中的当前事务的一些信息。将旧的事务对象信息封装到挂起对象中，最终会绑定到当前事务对象。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">String</span> <span class="n">name</span> <span class="o">=</span> <span class="n">TransactionSynchronizationManager</span><span class="o">.</span><span class="na">getCurrentTransactionName</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">				<span class="n">TransactionSynchronizationManager</span><span class="o">.</span><span class="na">setCurrentTransactionName</span><span class="o">(</span><span class="kc">null</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="kt">boolean</span> <span class="n">readOnly</span> <span class="o">=</span> <span class="n">TransactionSynchronizationManager</span><span class="o">.</span><span class="na">isCurrentTransactionReadOnly</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">				<span class="n">TransactionSynchronizationManager</span><span class="o">.</span><span class="na">setCurrentTransactionReadOnly</span><span class="o">(</span><span class="kc">false</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="n">Integer</span> <span class="n">isolationLevel</span> <span class="o">=</span> <span class="n">TransactionSynchronizationManager</span><span class="o">.</span><span class="na">getCurrentTransactionIsolationLevel</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">				<span class="n">TransactionSynchronizationManager</span><span class="o">.</span><span class="na">setCurrentTransactionIsolationLevel</span><span class="o">(</span><span class="kc">null</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="kt">boolean</span> <span class="n">wasActive</span> <span class="o">=</span> <span class="n">TransactionSynchronizationManager</span><span class="o">.</span><span class="na">isActualTransactionActive</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">				<span class="n">TransactionSynchronizationManager</span><span class="o">.</span><span class="na">setActualTransactionActive</span><span class="o">(</span><span class="kc">false</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 返回一个挂起资源持有对象，这个对象中封装了当前已存在事务的具体信息。这个对象会存储到新开启事务的TransactionStatus中。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="k">return</span> <span class="k">new</span> <span class="n">SuspendedResourcesHolder</span><span class="o">(</span>
</span></span><span class="line"><span class="cl">						<span class="n">suspendedResources</span><span class="o">,</span> <span class="n">suspendedSynchronizations</span><span class="o">,</span> <span class="n">name</span><span class="o">,</span> <span class="n">readOnly</span><span class="o">,</span> <span class="n">isolationLevel</span><span class="o">,</span> <span class="n">wasActive</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="k">catch</span> <span class="o">(</span><span class="n">RuntimeException</span> <span class="o">|</span> <span class="n">Error</span> <span class="n">ex</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// doSuspend failed - original transaction is still active...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">doResumeSynchronization</span><span class="o">(</span><span class="n">suspendedSynchronizations</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="k">throw</span> <span class="n">ex</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">else</span> <span class="k">if</span> <span class="o">(</span><span class="n">transaction</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// Transaction active but no synchronization active.
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="n">Object</span> <span class="n">suspendedResources</span> <span class="o">=</span> <span class="n">doSuspend</span><span class="o">(</span><span class="n">transaction</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="k">return</span> <span class="k">new</span> <span class="n">SuspendedResourcesHolder</span><span class="o">(</span><span class="n">suspendedResources</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">else</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// Neither transaction nor synchronization active.
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="k">return</span> <span class="kc">null</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>这个方法中，首先会挂起前一个事务，并把前一个事务信息返回，最终封装到SuspendedResourcesHolder中，之后会将 SuspendedResourcesHolder 封装到当前事务对象中。</p>
<p>在封装之前，会清除 TransactionSynchronizationManager 中记载的当前事务的一些信息。</p>
<p>具体的挂起操作，就在 doSuspend() 中：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">DataSourceTransactionManager</span> <span class="kd">extends</span> <span class="n">AbstractPlatformTransactionManager</span>
</span></span><span class="line"><span class="cl">		<span class="kd">implements</span> <span class="n">ResourceTransactionManager</span><span class="o">,</span> <span class="n">InitializingBean</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">	<span class="nd">@Override</span>
</span></span><span class="line"><span class="cl">	<span class="kd">protected</span> <span class="n">Object</span> <span class="nf">doSuspend</span><span class="o">(</span><span class="n">Object</span> <span class="n">transaction</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="n">DataSourceTransactionObject</span> <span class="n">txObject</span> <span class="o">=</span> <span class="o">(</span><span class="n">DataSourceTransactionObject</span><span class="o">)</span> <span class="n">transaction</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">		<span class="n">txObject</span><span class="o">.</span><span class="na">setConnectionHolder</span><span class="o">(</span><span class="kc">null</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 解绑链接资源
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">return</span> <span class="n">TransactionSynchronizationManager</span><span class="o">.</span><span class="na">unbindResource</span><span class="o">(</span><span class="n">obtainDataSource</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>可以看到，所谓的挂起，就是解绑resource，它存储在一个线程绑定的静态常量中。</p>
<p>来到 unbindResource()：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">DataSourceTransactionManager</span> <span class="kd">extends</span> <span class="n">AbstractPlatformTransactionManager</span>
</span></span><span class="line"><span class="cl">		<span class="kd">implements</span> <span class="n">ResourceTransactionManager</span><span class="o">,</span> <span class="n">InitializingBean</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kd">static</span> <span class="n">Object</span> <span class="nf">doUnbindResource</span><span class="o">(</span><span class="n">Object</span> <span class="n">actualKey</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">        <span class="c1">// 从ThreadLocal的map缓存中获取，如果为空，直接返回，如果不为空，则移除绑定关系。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>        <span class="n">Map</span><span class="o">&lt;</span><span class="n">Object</span><span class="o">,</span> <span class="n">Object</span><span class="o">&gt;</span> <span class="n">map</span> <span class="o">=</span> <span class="n">resources</span><span class="o">.</span><span class="na">get</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">        <span class="k">if</span> <span class="o">(</span><span class="n">map</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">            <span class="k">return</span> <span class="kc">null</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">        <span class="o">}</span>
</span></span><span class="line"><span class="cl">        <span class="c1">// 这里会解绑当前线程的链接资源。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>        <span class="n">Object</span> <span class="n">value</span> <span class="o">=</span> <span class="n">map</span><span class="o">.</span><span class="na">remove</span><span class="o">(</span><span class="n">actualKey</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">        <span class="c1">// Remove entire ThreadLocal if empty...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>        <span class="k">if</span> <span class="o">(</span><span class="n">map</span><span class="o">.</span><span class="na">isEmpty</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">            <span class="n">resources</span><span class="o">.</span><span class="na">remove</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">        <span class="o">}</span>
</span></span><span class="line"><span class="cl">        <span class="c1">// Transparently suppress a ResourceHolder that was marked as void...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>        <span class="k">if</span> <span class="o">(</span><span class="n">value</span> <span class="k">instanceof</span> <span class="n">ResourceHolder</span> <span class="o">&amp;&amp;</span> <span class="o">((</span><span class="n">ResourceHolder</span><span class="o">)</span> <span class="n">value</span><span class="o">).</span><span class="na">isVoid</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">            <span class="n">value</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">        <span class="o">}</span>
</span></span><span class="line"><span class="cl">        <span class="k">if</span> <span class="o">(</span><span class="n">value</span> <span class="o">!=</span> <span class="kc">null</span> <span class="o">&amp;&amp;</span> <span class="n">logger</span><span class="o">.</span><span class="na">isTraceEnabled</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">            <span class="n">logger</span><span class="o">.</span><span class="na">trace</span><span class="o">(</span><span class="s">&#34;Removed value [&#34;</span> <span class="o">+</span> <span class="n">value</span> <span class="o">+</span> <span class="s">&#34;] for key [&#34;</span> <span class="o">+</span> <span class="n">actualKey</span> <span class="o">+</span> <span class="s">&#34;] from thread [&#34;</span> <span class="o">+</span>
</span></span><span class="line"><span class="cl">                    <span class="n">Thread</span><span class="o">.</span><span class="na">currentThread</span><span class="o">().</span><span class="na">getName</span><span class="o">()</span> <span class="o">+</span> <span class="s">&#34;]&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">        <span class="o">}</span>
</span></span><span class="line"><span class="cl">        <span class="k">return</span> <span class="n">value</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">    <span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>事务的挂起，实际上就是将 DataSourceTransactionManager 中的静态常量 resources 中存储的值给移除掉。这是一个 ThreadLocal 类型的 map。</p>
<p>其定义是这样的：<code>private static final ThreadLocal&lt;Map&lt;Object, Object&gt;&gt; resources = new NamedThreadLocal&lt;&gt;(&quot;Transactional resources&quot;);</code></p>
<h2 id="2-事务的提交">2 事务的提交</h2>
<p>在执行完被代理方法后，最终会在 finally 语句块中调用 commitTransactionAfterReturning()，这个方法就完成了事务的提交操作。</p>
<p>源码如下：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">TransactionAspectSupport</span> <span class="kd">implements</span> <span class="n">BeanFactoryAware</span><span class="o">,</span> <span class="n">InitializingBean</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">    <span class="kd">protected</span> <span class="kt">void</span> <span class="nf">commitTransactionAfterReturning</span><span class="o">(</span><span class="nd">@Nullable</span> <span class="n">TransactionInfo</span> <span class="n">txInfo</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="k">if</span> <span class="o">(</span><span class="n">txInfo</span> <span class="o">!=</span> <span class="kc">null</span> <span class="o">&amp;&amp;</span> <span class="n">txInfo</span><span class="o">.</span><span class="na">getTransactionStatus</span><span class="o">()</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">            <span class="k">if</span> <span class="o">(</span><span class="n">logger</span><span class="o">.</span><span class="na">isTraceEnabled</span><span class="o">())</span> <span class="o">{</span> <span class="n">logger</span><span class="o">.</span><span class="na">trace</span><span class="o">(</span><span class="s">&#34;Completing transaction for [&#34;</span> <span class="o">+</span> <span class="n">txInfo</span><span class="o">.</span><span class="na">getJoinpointIdentification</span><span class="o">()</span> <span class="o">+</span> <span class="s">&#34;]&#34;</span><span class="o">);</span> <span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// 使用事务管理器，提交事务。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="n">txInfo</span><span class="o">.</span><span class="na">getTransactionManager</span><span class="o">().</span><span class="na">commit</span><span class="o">(</span><span class="n">txInfo</span><span class="o">.</span><span class="na">getTransactionStatus</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>其实这个方法中，不一定就是提交事务，如果设置了仅回滚，则会进行回滚操作。</p>
<p>具体逻辑在 commit()中：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">AbstractPlatformTransactionManager</span> <span class="kd">implements</span> <span class="n">PlatformTransactionManager</span><span class="o">,</span> <span class="n">Serializable</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">   <span class="nd">@Override</span>
</span></span><span class="line"><span class="cl">   	<span class="kd">public</span> <span class="kd">final</span> <span class="kt">void</span> <span class="nf">commit</span><span class="o">(</span><span class="n">TransactionStatus</span> <span class="n">status</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">TransactionException</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">   		<span class="k">if</span> <span class="o">(</span><span class="n">status</span><span class="o">.</span><span class="na">isCompleted</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">   			<span class="k">throw</span> <span class="k">new</span> <span class="n">IllegalTransactionStateException</span><span class="o">(</span>
</span></span><span class="line"><span class="cl">   					<span class="s">&#34;Transaction is already completed - do not call commit or rollback more than once per transaction&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">   		<span class="o">}</span>
</span></span><span class="line"><span class="cl">   
</span></span><span class="line"><span class="cl">   		<span class="n">DefaultTransactionStatus</span> <span class="n">defStatus</span> <span class="o">=</span> <span class="o">(</span><span class="n">DefaultTransactionStatus</span><span class="o">)</span> <span class="n">status</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">   		<span class="c1">// TODO 如果事务信息中保存的是仅回滚，则进行回滚操作。比如假如到这个事务中的方法抛出异常，
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>   		<span class="c1">//  则不会再那个方法就回滚，而是返回到事务的起点方法后，再进行回滚操作。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>   		<span class="k">if</span> <span class="o">(</span><span class="n">defStatus</span><span class="o">.</span><span class="na">isLocalRollbackOnly</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">   			<span class="k">if</span> <span class="o">(</span><span class="n">defStatus</span><span class="o">.</span><span class="na">isDebug</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">   				<span class="n">logger</span><span class="o">.</span><span class="na">debug</span><span class="o">(</span><span class="s">&#34;Transactional code has requested rollback&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">   			<span class="o">}</span>
</span></span><span class="line"><span class="cl">   			<span class="c1">// 回滚事务
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>   			<span class="n">processRollback</span><span class="o">(</span><span class="n">defStatus</span><span class="o">,</span> <span class="kc">false</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">   			<span class="k">return</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">   		<span class="o">}</span>
</span></span><span class="line"><span class="cl">   		<span class="c1">// 判断是否仅回滚，主要是看connectionHolder是否设置了仅回滚。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>   		<span class="k">if</span> <span class="o">(!</span><span class="n">shouldCommitOnGlobalRollbackOnly</span><span class="o">()</span> <span class="o">&amp;&amp;</span> <span class="n">defStatus</span><span class="o">.</span><span class="na">isGlobalRollbackOnly</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">   			<span class="k">if</span> <span class="o">(</span><span class="n">defStatus</span><span class="o">.</span><span class="na">isDebug</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">   				<span class="n">logger</span><span class="o">.</span><span class="na">debug</span><span class="o">(</span><span class="s">&#34;Global transaction is marked as rollback-only but transactional code requested commit&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">   			<span class="o">}</span>
</span></span><span class="line"><span class="cl">   			<span class="c1">// 回滚事务
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>   			<span class="n">processRollback</span><span class="o">(</span><span class="n">defStatus</span><span class="o">,</span> <span class="kc">true</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">   			<span class="k">return</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">   		<span class="o">}</span>
</span></span><span class="line"><span class="cl">   		<span class="c1">// TODO 事务提交
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>   		<span class="n">processCommit</span><span class="o">(</span><span class="n">defStatus</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">   	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>比如 RERUIRED 传播行为，前一个方法已经开启了事务，然后当前方法就会加入到这个已存在的事务中。如果这个内层的方法抛出异常，即使在外层方法中捕获异常，同样会回滚事务。</p>
<p>这个回滚操作并不是在内层方法中做的，在内层方法结束的时候，只会做一个 rollbackOnly 的标记。真正的回滚是在创建事务的起点方法做的。</p>
<p>所以上面代码中，会先判断是否仅回滚，如果是，则直接执行回滚操作。isGlobalRollbackOnly() 的判断于此类似。如果最终判断应该提交事务，则执行 processCommit() 进行事务的提交。</p>
<p>来到 processCommit() 源码：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">AbstractPlatformTransactionManager</span> <span class="kd">implements</span> <span class="n">PlatformTransactionManager</span><span class="o">,</span> <span class="n">Serializable</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kt">void</span> <span class="nf">processCommit</span><span class="o">(</span><span class="n">DefaultTransactionStatus</span> <span class="n">status</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">TransactionException</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="k">try</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="kt">boolean</span> <span class="n">beforeCompletionInvoked</span> <span class="o">=</span> <span class="kc">false</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">			<span class="k">try</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="kt">boolean</span> <span class="n">unexpectedRollback</span> <span class="o">=</span> <span class="kc">false</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 预提交，这是一个钩子方法，点进去可以看到是一个空方法。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">prepareForCommit</span><span class="o">(</span><span class="n">status</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="c1">//  TransactionSynchronization的扩展点可在事务方法中向TransactionSynchronizationManager注入回调。不同的方法回调时机不一样。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="c1">// 也可以使用 @TransactionalEventListener，其原理也是注入 TransactionSynchronization 回调。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="c1">// 事务同步回调接口TransactionSynchronization.beforeCommit()的调用。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">triggerBeforeCommit</span><span class="o">(</span><span class="n">status</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 事务同步回调接口TransactionSynchronization.beforeCompletion()的调用。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">triggerBeforeCompletion</span><span class="o">(</span><span class="n">status</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="n">beforeCompletionInvoked</span> <span class="o">=</span> <span class="kc">true</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">				<span class="c1">// TODO 是否有回滚点（保存点），如果是设置了回滚点，则仅仅吧回滚点抹除即可。真正的提交是在最外层事务提交做的。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="c1">//  这也是NESTED传播行为，在外围方法事务异常时，所有嵌套事务全部回滚的原因所在。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="k">if</span> <span class="o">(</span><span class="n">status</span><span class="o">.</span><span class="na">hasSavepoint</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="k">if</span> <span class="o">(</span><span class="n">status</span><span class="o">.</span><span class="na">isDebug</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">						<span class="n">logger</span><span class="o">.</span><span class="na">debug</span><span class="o">(</span><span class="s">&#34;Releasing transaction savepoint&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">					<span class="o">}</span>
</span></span><span class="line"><span class="cl">					<span class="n">unexpectedRollback</span> <span class="o">=</span> <span class="n">status</span><span class="o">.</span><span class="na">isGlobalRollbackOnly</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">					<span class="n">status</span><span class="o">.</span><span class="na">releaseHeldSavepoint</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span> <span class="k">else</span> <span class="k">if</span> <span class="o">(</span><span class="n">status</span><span class="o">.</span><span class="na">isNewTransaction</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="k">if</span> <span class="o">(</span><span class="n">status</span><span class="o">.</span><span class="na">isDebug</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">						<span class="n">logger</span><span class="o">.</span><span class="na">debug</span><span class="o">(</span><span class="s">&#34;Initiating transaction commit&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">					<span class="o">}</span>
</span></span><span class="line"><span class="cl">					<span class="c1">// TODO 事务提交
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>					<span class="n">unexpectedRollback</span> <span class="o">=</span> <span class="n">status</span><span class="o">.</span><span class="na">isGlobalRollbackOnly</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">					<span class="n">doCommit</span><span class="o">(</span><span class="n">status</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span><span class="k">else</span> <span class="k">if</span> <span class="o">(</span><span class="n">isFailEarlyOnGlobalRollbackOnly</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="n">unexpectedRollback</span> <span class="o">=</span> <span class="n">status</span><span class="o">.</span><span class="na">isGlobalRollbackOnly</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">			    <span class="c1">// 省略...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="o">}</span><span class="c1">// 省略... 这里会有一些catch，对 TransactionSynchronization 扩展点的调用。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="k">finally</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// TransactionSynchronization 扩展
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">triggerAfterCompletion</span><span class="o">(</span><span class="n">status</span><span class="o">,</span> <span class="n">TransactionSynchronization</span><span class="o">.</span><span class="na">STATUS_COMMITTED</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">finally</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">cleanupAfterCompletion</span><span class="o">(</span><span class="n">status</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><ol>
<li>在 processCommit() 中，会先进行一些扩展钩子方法的回调。这里使用了策略模式，会对 synchronizations 遍历，里面封装了所有注册的 TransactionSynchronization，遍历去调用对应的方法。</li>
<li>如果设置了保存点，则将保存点抹除。在 NESTED 传播行为中，它的实现就是使用的保存点（savePoint），NESTED 传播行为并不会新启一个事务，而是标记一个 savePoint，如果这个方法异常，就会回滚至 savePoint处。</li>
<li>如果是一个事务创建的起点，就会执行提交操作。</li>
</ol>
<p>在 doCommit() 中进行了事务的提交：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">DataSourceTransactionManager</span> <span class="kd">extends</span> <span class="n">AbstractPlatformTransactionManager</span>
</span></span><span class="line"><span class="cl">		<span class="kd">implements</span> <span class="n">ResourceTransactionManager</span><span class="o">,</span> <span class="n">InitializingBean</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">    <span class="nd">@Override</span>
</span></span><span class="line"><span class="cl">	<span class="kd">protected</span> <span class="kt">void</span> <span class="nf">doCommit</span><span class="o">(</span><span class="n">DefaultTransactionStatus</span> <span class="n">status</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 获取到事务的链接对象，提交事务
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">DataSourceTransactionObject</span> <span class="n">txObject</span> <span class="o">=</span> <span class="o">(</span><span class="n">DataSourceTransactionObject</span><span class="o">)</span> <span class="n">status</span><span class="o">.</span><span class="na">getTransaction</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">		<span class="n">Connection</span> <span class="n">con</span> <span class="o">=</span> <span class="n">txObject</span><span class="o">.</span><span class="na">getConnectionHolder</span><span class="o">().</span><span class="na">getConnection</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">		<span class="n">con</span><span class="o">.</span><span class="na">commit</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>从上面源码可以看到，拿到事务对象，从事务对象中拿到 ConnectionHolder，在拿到 Connection，使用 Connection 调用 commit() 进行事务的提交。</p>
<h2 id="3-事务的回滚">3 事务的回滚</h2>
<p>在调用业务方法抛出异常时，事务的通知方法中，会捕获这个异常。然后对事务进行回滚操作，之后将异常再次抛出。</p>
<p>事务的回滚入口方法在 completeTransactionAfterThrowing()：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">TransactionAspectSupport</span> <span class="kd">implements</span> <span class="n">BeanFactoryAware</span><span class="o">,</span> <span class="n">InitializingBean</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">    <span class="kd">protected</span> <span class="kt">void</span> <span class="nf">completeTransactionAfterThrowing</span><span class="o">(</span><span class="nd">@Nullable</span> <span class="n">TransactionInfo</span> <span class="n">txInfo</span><span class="o">,</span> <span class="n">Throwable</span> <span class="n">ex</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 如果存在事务状态对象
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">if</span> <span class="o">(</span><span class="n">txInfo</span> <span class="o">!=</span> <span class="kc">null</span> <span class="o">&amp;&amp;</span> <span class="n">txInfo</span><span class="o">.</span><span class="na">getTransactionStatus</span><span class="o">()</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// 判断事务属性不为空并且满足回滚规则，就进行回滚，否则进行事务提交
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="k">if</span> <span class="o">(</span><span class="n">txInfo</span><span class="o">.</span><span class="na">transactionAttribute</span> <span class="o">!=</span> <span class="kc">null</span> <span class="o">&amp;&amp;</span> <span class="n">txInfo</span><span class="o">.</span><span class="na">transactionAttribute</span><span class="o">.</span><span class="na">rollbackOn</span><span class="o">(</span><span class="n">ex</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="c1">// TODO 重点：具体的回滚代码
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>                <span class="n">txInfo</span><span class="o">.</span><span class="na">getTransactionManager</span><span class="o">().</span><span class="na">rollback</span><span class="o">(</span><span class="n">txInfo</span><span class="o">.</span><span class="na">getTransactionStatus</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 省略 try catch 块...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="o">}</span><span class="k">else</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">                <span class="c1">// 如果抛出的异常，与回滚的异常定义不匹配，则提交事务。也就是说，抛出异常了，也不一定回滚。它存在一个异常类型匹配。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>                <span class="n">txInfo</span><span class="o">.</span><span class="na">getTransactionManager</span><span class="o">().</span><span class="na">commit</span><span class="o">(</span><span class="n">txInfo</span><span class="o">.</span><span class="na">getTransactionStatus</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">			    <span class="c1">// 这里省略了 try catch 块...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>首先判断是否存在事务，如果存在事务，则判断，抛出的异常是否符合是需要回滚的异常。</p>
<p>具体哪些异常回滚是可以设置的，如果不设置，默认是 RuntimeException 和 Error。</p>
<p>简单看下 rollBackOn()：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">RuleBasedTransactionAttribute</span> <span class="kd">extends</span> <span class="n">DefaultTransactionAttribute</span> <span class="kd">implements</span> <span class="n">Serializable</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="nd">@Override</span>
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="kt">boolean</span> <span class="nf">rollbackOn</span><span class="o">(</span><span class="n">Throwable</span> <span class="n">ex</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="n">RollbackRuleAttribute</span> <span class="n">winner</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">		<span class="kt">int</span> <span class="n">deepest</span> <span class="o">=</span> <span class="n">Integer</span><span class="o">.</span><span class="na">MAX_VALUE</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">		<span class="c1">// 判断回滚规则
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">if</span> <span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">rollbackRules</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">for</span> <span class="o">(</span><span class="n">RollbackRuleAttribute</span> <span class="n">rule</span> <span class="o">:</span> <span class="k">this</span><span class="o">.</span><span class="na">rollbackRules</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 递归调用异常的父类，如果异常名称中包含规则中封装的异常名称，则返回。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="kt">int</span> <span class="n">depth</span> <span class="o">=</span> <span class="n">rule</span><span class="o">.</span><span class="na">getDepth</span><span class="o">(</span><span class="n">ex</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 如果不满足规则，会返回-1，如果满足了规则，会把这个规则赋值到winner临时变量中。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="k">if</span> <span class="o">(</span><span class="n">depth</span> <span class="o">&gt;=</span> <span class="n">0</span> <span class="o">&amp;&amp;</span> <span class="n">depth</span> <span class="o">&lt;</span> <span class="n">deepest</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="n">deepest</span> <span class="o">=</span> <span class="n">depth</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">					<span class="n">winner</span> <span class="o">=</span> <span class="n">rule</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">		<span class="k">if</span> <span class="o">(</span><span class="n">logger</span><span class="o">.</span><span class="na">isTraceEnabled</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">logger</span><span class="o">.</span><span class="na">trace</span><span class="o">(</span><span class="s">&#34;Winning rollback rule is: &#34;</span> <span class="o">+</span> <span class="n">winner</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">		<span class="c1">// 如果没有配置回滚异常或不回滚异常，则会走默认的。默认回滚运行时异常及Error：
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="c1">// (ex instanceof RuntimeException || ex instanceof Error);
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="c1">// User superclass behavior (rollback on unchecked) if no rule matches.
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">if</span> <span class="o">(</span><span class="n">winner</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">logger</span><span class="o">.</span><span class="na">trace</span><span class="o">(</span><span class="s">&#34;No relevant rollback rule found: applying default rules&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="k">return</span> <span class="kd">super</span><span class="o">.</span><span class="na">rollbackOn</span><span class="o">(</span><span class="n">ex</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 判断规则如果是不回滚规则，则返回false，表示不需要回滚。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="c1">// 判断规则如果不是不回滚规则，返回true，表示需要回滚
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">return</span> <span class="o">!(</span><span class="n">winner</span> <span class="k">instanceof</span> <span class="n">NoRollbackRuleAttribute</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>如果事务声明中配置了需要回滚的异常，就递归的匹配异常，获取其 RollbackRuleAttribute，如果获取的到，返回这个规则不属于不回滚的异常规则 true/fasle。</p>
<p>如果匹配不到，就使用默认的回滚规则，默认回滚规则在 <code>super.rollbackOn(ex);</code> 中定义了。</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">DefaultTransactionAttribute</span> <span class="kd">extends</span> <span class="n">DefaultTransactionDefinition</span> <span class="kd">implements</span> <span class="n">TransactionAttribute</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">    <span class="nd">@Override</span>
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="kt">boolean</span> <span class="nf">rollbackOn</span><span class="o">(</span><span class="n">Throwable</span> <span class="n">ex</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="k">return</span> <span class="o">(</span><span class="n">ex</span> <span class="k">instanceof</span> <span class="n">RuntimeException</span> <span class="o">||</span> <span class="n">ex</span> <span class="k">instanceof</span> <span class="n">Error</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>回到 completeTransactionAfterThrowing() 中，接着看具体的回滚逻辑 rollback()，在这里会调用到 processRollback()。</p>
<p>源码如下：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">AbstractPlatformTransactionManager</span> <span class="kd">implements</span> <span class="n">PlatformTransactionManager</span><span class="o">,</span> <span class="n">Serializable</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">    <span class="kd">private</span> <span class="kt">void</span> <span class="nf">processRollback</span><span class="o">(</span><span class="n">DefaultTransactionStatus</span> <span class="n">status</span><span class="o">,</span> <span class="kt">boolean</span> <span class="n">unexpected</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">        <span class="k">try</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">            <span class="kt">boolean</span> <span class="n">unexpectedRollback</span> <span class="o">=</span> <span class="n">unexpected</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">            <span class="k">try</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">                <span class="c1">// 如果是一个新建的事务，即到了事务的起点。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>                <span class="c1">// 在回滚之前会循环调用TransactionSynchronization的beforeCompletion方法，这里是一个回调函数
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>                <span class="n">triggerBeforeCompletion</span><span class="o">(</span><span class="n">status</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">                <span class="c1">// 有保存点（或者叫回滚点），回滚到保存点位置
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>                <span class="k">if</span> <span class="o">(</span><span class="n">status</span><span class="o">.</span><span class="na">hasSavepoint</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">                    <span class="k">if</span> <span class="o">(</span><span class="n">status</span><span class="o">.</span><span class="na">isDebug</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">                        <span class="n">logger</span><span class="o">.</span><span class="na">debug</span><span class="o">(</span><span class="s">&#34;Rolling back transaction to savepoint&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">                    <span class="o">}</span>
</span></span><span class="line"><span class="cl">                    <span class="n">status</span><span class="o">.</span><span class="na">rollbackToHeldSavepoint</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">                <span class="o">}</span><span class="c1">// 如果是一个新建的事务，即回到了事务的起点。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>                <span class="k">else</span> <span class="k">if</span> <span class="o">(</span><span class="n">status</span><span class="o">.</span><span class="na">isNewTransaction</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">                    <span class="k">if</span> <span class="o">(</span><span class="n">status</span><span class="o">.</span><span class="na">isDebug</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">                        <span class="n">logger</span><span class="o">.</span><span class="na">debug</span><span class="o">(</span><span class="s">&#34;Initiating transaction rollback&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">                    <span class="o">}</span>
</span></span><span class="line"><span class="cl">                    <span class="c1">// 从当前事务状态对象中获取到链接对象，进行回滚操作
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>                    <span class="n">doRollback</span><span class="o">(</span><span class="n">status</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">                <span class="o">}</span>
</span></span><span class="line"><span class="cl">                <span class="k">else</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">                    <span class="c1">// 如果是加入的已有事务，则将事务状态设置为仅回滚 rollbackOnly=true，最终返回到事务的起点时，是否向外抛出异常都会回滚。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>                    <span class="c1">// 所以在 REQUIRED 传播行为中，任何一个加入事务的方法异常，都会触发回滚。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>                    <span class="c1">// Participating in larger transaction
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>                    <span class="k">if</span> <span class="o">(</span><span class="n">status</span><span class="o">.</span><span class="na">hasTransaction</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">                        <span class="k">if</span> <span class="o">(</span><span class="n">status</span><span class="o">.</span><span class="na">isLocalRollbackOnly</span><span class="o">()</span> <span class="o">||</span> <span class="n">isGlobalRollbackOnParticipationFailure</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">                            <span class="k">if</span> <span class="o">(</span><span class="n">status</span><span class="o">.</span><span class="na">isDebug</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">                                <span class="n">logger</span><span class="o">.</span><span class="na">debug</span><span class="o">(</span><span class="s">&#34;Participating transaction failed - marking existing transaction as rollback-only&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">                            <span class="o">}</span>
</span></span><span class="line"><span class="cl">                            <span class="n">doSetRollbackOnly</span><span class="o">(</span><span class="n">status</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">                        <span class="o">}</span>
</span></span><span class="line"><span class="cl">                        <span class="k">else</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">                            <span class="k">if</span> <span class="o">(</span><span class="n">status</span><span class="o">.</span><span class="na">isDebug</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">                                <span class="n">logger</span><span class="o">.</span><span class="na">debug</span><span class="o">(</span><span class="s">&#34;Participating transaction failed - letting transaction originator decide on rollback&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">                            <span class="o">}</span>
</span></span><span class="line"><span class="cl">                        <span class="o">}</span>
</span></span><span class="line"><span class="cl">                    <span class="o">}</span>
</span></span><span class="line"><span class="cl">                    <span class="k">else</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">                        <span class="n">logger</span><span class="o">.</span><span class="na">debug</span><span class="o">(</span><span class="s">&#34;Should roll back transaction but cannot - no transaction available&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">                    <span class="o">}</span>
</span></span><span class="line"><span class="cl">                    <span class="c1">// Unexpected rollback only matters here if we&#39;re asked to fail early
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>                    <span class="k">if</span> <span class="o">(!</span><span class="n">isFailEarlyOnGlobalRollbackOnly</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">                        <span class="n">unexpectedRollback</span> <span class="o">=</span> <span class="kc">false</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">                    <span class="o">}</span>
</span></span><span class="line"><span class="cl">                <span class="o">}</span>
</span></span><span class="line"><span class="cl">            <span class="o">}</span>
</span></span><span class="line"><span class="cl">            <span class="k">catch</span> <span class="o">(</span><span class="n">RuntimeException</span> <span class="o">|</span> <span class="n">Error</span> <span class="n">ex</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">                <span class="c1">// TransactionSynchronization 扩展点
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>                <span class="n">triggerAfterCompletion</span><span class="o">(</span><span class="n">status</span><span class="o">,</span> <span class="n">TransactionSynchronization</span><span class="o">.</span><span class="na">STATUS_UNKNOWN</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">                <span class="k">throw</span> <span class="n">ex</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">            <span class="o">}</span>
</span></span><span class="line"><span class="cl">            <span class="c1">// 事务提交后，获取事务同步器进行循环调用，TransactionSynchronization.afterCompletion
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>            <span class="n">triggerAfterCompletion</span><span class="o">(</span><span class="n">status</span><span class="o">,</span> <span class="n">TransactionSynchronization</span><span class="o">.</span><span class="na">STATUS_ROLLED_BACK</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">            <span class="c1">// Raise UnexpectedRollbackException if we had a global rollback-only marker
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>            <span class="k">if</span> <span class="o">(</span><span class="n">unexpectedRollback</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">                <span class="k">throw</span> <span class="k">new</span> <span class="n">UnexpectedRollbackException</span><span class="o">(</span>
</span></span><span class="line"><span class="cl">                        <span class="s">&#34;Transaction rolled back because it has been marked as rollback-only&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">            <span class="o">}</span>
</span></span><span class="line"><span class="cl">        <span class="o">}</span>
</span></span><span class="line"><span class="cl">        <span class="k">finally</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">            <span class="n">cleanupAfterCompletion</span><span class="o">(</span><span class="n">status</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">        <span class="o">}</span>
</span></span><span class="line"><span class="cl">    <span class="o">}</span>  
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>流程如下：</p>
<ol>
<li>首先执行已注册的 TransactionSynchronization 的一些回调方法。</li>
<li>如果当前事务中有保存点（savePoint），就回滚至保存点。最终会通过 JDBC 来进行回滚。</li>
<li>如果当前事务是一个事务创建的起点，就回滚事务。</li>
<li>执行一些已注册的 TransactionSynchronization 进行后置处理。</li>
</ol>
<p>doRollback() 源码如下：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">AbstractPlatformTransactionManager</span> <span class="kd">implements</span> <span class="n">PlatformTransactionManager</span><span class="o">,</span> <span class="n">Serializable</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">    <span class="nd">@Override</span>
</span></span><span class="line"><span class="cl">	<span class="kd">protected</span> <span class="kt">void</span> <span class="nf">doRollback</span><span class="o">(</span><span class="n">DefaultTransactionStatus</span> <span class="n">status</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 从事务状态对象中获取当前持有的链接，进行回滚操作
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">DataSourceTransactionObject</span> <span class="n">txObject</span> <span class="o">=</span> <span class="o">(</span><span class="n">DataSourceTransactionObject</span><span class="o">)</span> <span class="n">status</span><span class="o">.</span><span class="na">getTransaction</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">		<span class="n">Connection</span> <span class="n">con</span> <span class="o">=</span> <span class="n">txObject</span><span class="o">.</span><span class="na">getConnectionHolder</span><span class="o">().</span><span class="na">getConnection</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">		<span class="n">con</span><span class="o">.</span><span class="na">rollback</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 省略 try catch 块...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>最终会调用 <code>con.rollback()</code> 进行事务的回滚。</p>
<p>而通过回滚点回滚，最终会调用到这里：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">JdbcTransactionObjectSupport</span> <span class="kd">implements</span> <span class="n">SavepointManager</span><span class="o">,</span> <span class="n">SmartTransactionObject</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">    <span class="nd">@Override</span>
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="kt">void</span> <span class="nf">rollbackToSavepoint</span><span class="o">(</span><span class="n">Object</span> <span class="n">savepoint</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">TransactionException</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="n">ConnectionHolder</span> <span class="n">conHolder</span> <span class="o">=</span> <span class="n">getConnectionHolderForSavepoint</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">        <span class="n">conHolder</span><span class="o">.</span><span class="na">getConnection</span><span class="o">().</span><span class="na">rollback</span><span class="o">((</span><span class="n">Savepoint</span><span class="o">)</span> <span class="n">savepoint</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">        <span class="n">conHolder</span><span class="o">.</span><span class="na">resetRollbackOnly</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 省略 try catch 块...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><h2 id="4-数据库连接的释放">4 数据库连接的释放</h2>
<p>无论是事务提交或是回滚，之后，都会调用一个方法 triggerAfterCompletion()，在这个方法中，就完成了数据库连接的释放。</p>
<p>在真正释放之前，同样也会调用已注册的 TransactionSynchronization 的一个扩展方法 resume()。</p>
<p>连接的释放，实际上就是通过 TransactionSynchronization 的扩展方法来实现的，这个方法是 afterCompletion()。</p>
<p>在 triggerAfterCompletion() 中，调用了 invokeAfterCompletion()。在这里就遍历了 synchronizations，进行 afterCompletion() 的调用。</p>
<p>源码如下（省略了try catch 代码块）：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">TransactionSynchronizationUtils</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="kd">static</span> <span class="kt">void</span> <span class="nf">invokeAfterCompletion</span><span class="o">(</span><span class="nd">@Nullable</span> <span class="n">List</span><span class="o">&lt;</span><span class="n">TransactionSynchronization</span><span class="o">&gt;</span> <span class="n">synchronizations</span><span class="o">,</span>
</span></span><span class="line"><span class="cl">			<span class="kt">int</span> <span class="n">completionStatus</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="k">if</span> <span class="o">(</span><span class="n">synchronizations</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">for</span> <span class="o">(</span><span class="n">TransactionSynchronization</span> <span class="n">synchronization</span> <span class="o">:</span> <span class="n">synchronizations</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="n">synchronization</span><span class="o">.</span><span class="na">afterCompletion</span><span class="o">(</span><span class="n">completionStatus</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><blockquote>
<p>在 afterCompletion() 中经历了以下调用链：</p>
<p>releaseConnection() -&gt; doReleaseConnection() -&gt; doCloseConnection() -&gt; con.close()</p>
</blockquote>
<p>以 druid 连接池为例，最终会调用到 recycle()，在recycle中，有这么一段代码：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">DruidDataSource</span> <span class="kd">extends</span> <span class="n">DruidAbstractDataSource</span> <span class="kd">implements</span> <span class="n">DruidDataSourceMBean</span><span class="o">,</span> <span class="n">ManagedDataSource</span><span class="o">,</span> <span class="n">Referenceable</span><span class="o">,</span> <span class="n">Closeable</span><span class="o">,</span> <span class="n">Cloneable</span><span class="o">,</span> <span class="n">ConnectionPoolDataSource</span><span class="o">,</span> <span class="n">MBeanRegistration</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kd">volatile</span> <span class="n">DruidConnectionHolder</span><span class="o">[]</span> <span class="n">connections</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">    <span class="c1">// 步骤一
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>    <span class="kd">protected</span> <span class="kt">void</span> <span class="nf">recycle</span><span class="o">(</span><span class="n">DruidPooledConnection</span> <span class="n">pooledConnection</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">SQLException</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">        <span class="c1">// 省略无关代码...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>        <span class="n">lock</span><span class="o">.</span><span class="na">lock</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">        <span class="k">try</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">            <span class="k">if</span> <span class="o">(</span><span class="n">holder</span><span class="o">.</span><span class="na">active</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">                <span class="n">activeCount</span><span class="o">--;</span>
</span></span><span class="line"><span class="cl">                <span class="n">holder</span><span class="o">.</span><span class="na">active</span> <span class="o">=</span> <span class="kc">false</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">            <span class="o">}</span>
</span></span><span class="line"><span class="cl">            <span class="n">closeCount</span><span class="o">++;</span>
</span></span><span class="line"><span class="cl">            <span class="c1">// 这个方法，将连接归还。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>            <span class="n">result</span> <span class="o">=</span> <span class="n">putLast</span><span class="o">(</span><span class="n">holder</span><span class="o">,</span> <span class="n">currentTimeMillis</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">            <span class="n">recycleCount</span><span class="o">++;</span>
</span></span><span class="line"><span class="cl">        <span class="o">}</span> <span class="k">finally</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">            <span class="n">lock</span><span class="o">.</span><span class="na">unlock</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">        <span class="o">}</span>
</span></span><span class="line"><span class="cl">        <span class="c1">//省略无关代码...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>    <span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">    <span class="c1">// 步骤二
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>    <span class="kt">boolean</span> <span class="nf">putLast</span><span class="o">(</span><span class="n">DruidConnectionHolder</span> <span class="n">e</span><span class="o">,</span> <span class="kt">long</span> <span class="n">lastActiveTimeMillis</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">        <span class="k">if</span> <span class="o">(</span><span class="n">poolingCount</span> <span class="o">&gt;=</span> <span class="n">maxActive</span> <span class="o">||</span> <span class="n">e</span><span class="o">.</span><span class="na">discard</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">            <span class="k">return</span> <span class="kc">false</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">        <span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">        <span class="n">e</span><span class="o">.</span><span class="na">lastActiveTimeMillis</span> <span class="o">=</span> <span class="n">lastActiveTimeMillis</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">        <span class="c1">// 这里，将连接归还到数组的指定索引处。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>        <span class="n">connections</span><span class="o">[</span><span class="n">poolingCount</span><span class="o">]</span> <span class="o">=</span> <span class="n">e</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">        <span class="n">incrementPoolingCount</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">        <span class="k">if</span> <span class="o">(</span><span class="n">poolingCount</span> <span class="o">&gt;</span> <span class="n">poolingPeak</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">            <span class="n">poolingPeak</span> <span class="o">=</span> <span class="n">poolingCount</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">            <span class="n">poolingPeakTime</span> <span class="o">=</span> <span class="n">lastActiveTimeMillis</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">        <span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">        <span class="n">notEmpty</span><span class="o">.</span><span class="na">signal</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">        <span class="n">notEmptySignalCount</span><span class="o">++;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">        <span class="k">return</span> <span class="kc">true</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">    <span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>从上面代码中可以看到，在 <code>result = putLast(holder, currentTimeMillis);</code> 中，就将连接进行回收了。</p></div>

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